The invention relates to a spring biased tensioner of the eccentric type with an effective pivot arm as part of a stub shaft and located within the inside diameter of a pulley bearing, but more particularly, the invention relates to an eccentric type tensioner with a damping mechanism utilizing friction surface sliding for inhibiting pivotal oscillations of the pivot arm.
Various mechanisms are used to inhibit angular movements of a tensioner's pivot arm about its pivot axis. An example of a non-eccentric type tensioner (i.e., where the pivot arm has a length that is greater than the radius of a pulley carried by the pivot arm) utilizing a cam activated damping mechanism is disclosed in U.S. Pat. No. 4,557,707. Besides its overall large size comparative to an eccentric type tensioner, the cam operated mechanism of the '707 tensioner operates at an effective radius that is less than the length of the tensioner's pivot arm which affects an insensitivity of the damping torque relative to the output torque of the tensioner as reacted through the pivot arm by way of a pulley.
Another problem associated with the size of the non-eccentric belt tensioner of the type disclosed in U.S. Pat. No. 4,557,707, is that the cam operated damping mechanism is located outside a radial boundary of the pulley.
Still another problem associated with the '707 tensioning device is that the cam mechanism includes a singular, polymeric cam ring in which cam followers in the form of bent tabs are located. With a single, plastic cam follower ring, it is difficult to change operating characteristics of the friction sliding surfaces, the slope of the surfaces, as the cam is in the form of bent tabs of metal.
An example of an eccentric type tensioner that includes a cam activated mechanism, is disclosed in U.S. Pat. No. 4,834,694. The cam activated mechanism of the tensioner does not operate to provide a variable axial force associated with damping pivotal movements of the pivot arm, but rather, the cam mechanism operates as a one-way clutch where a radial force is generated to move a follower to lockup with an inner surface of a pulley supporting housing whereby movements of the pivot arm in a non-tensioning direction, are prevented or substantially inhibited.
Another example of an eccentric type tensioner is disclosed in U.S. Pat. No. 4,808,148. While a cam operated mechanism is not used, a locking mechanism in the form of a ratchet and pawl, is used to prevent the pivot arm from rotating in a non-tensioning direction which is similar to the operation of the aforementioned '694 tensioner. However, the '148 device presents a size problem in that the rachet and pawl mechanism is located within the inside diameter of a pulley bearing making the bearing overly large and expensive in comparison to other eccentric type tensioning devices that are without additional mechanisms located within a bearing bore.
Still another problem associated with the aforementioned tensioners is that the location of friction sliding surfaces are at an effective radius that is equal to less than the length of the pivot arm, or the inside radius of its pulley bearing.
The present invention primarily concerns belt tensioners of the eccentric category and makes possible the use of small pulley bearings.